The principle that the Supreme Court established in this case was the principle of judicial review. Judicial review is the idea that the judicial branch has the right to determine if laws passed by Congress are constitutional and to strike them down if they are not.

In the Constitution, there is no mention of judicial review. The Framers did not specify who was to have the power to decide when a law was or was not constitutional. In this case, Chief Justice John Marshall wrote an opinion in which he claimed that power for the judicial branch. Since then, this principle has come to be accepted and we take for granted that the courts have this power today.